Interpretive Summary: Toxoplasma gondii is a single-celled parasite of all warm-blooded hosts worldwide. It causes mental retardation and loss of vision in children, and abortion in livestock. Cats are the main
reservoir of T. gondii because they are the only hosts that can excrete the resistant stage (oocyst) of the parasite in the feces. Humans become infected by eating under cooked meat from
infected animals and food and water contaminated with oocysts. Humans can also get toxoplasmosis by petting dogs that have rolled over in infected cat feces. Stray dogs are also considered as sentinels (indicators) in the epidemiology of Toxoplasma gondii because they are carnivores and eat variety of foods, including garbage. In the present study, authors found a very high (50 of 51) prevalence of T. gondii infection in dogs in stray dogs from Egypt. The results will be of interest to biologists, parasitologists, and public health workers.

Technical Abstract:
Stray dogs are considered as sentinels in the epidemiology of Toxoplasma gondii because they are carnivores and eat variety of foods, including garbage. In the present study, tissues and sera of 51 stray dogs (Canis familiaris) from Giza, Egypt were examined for T. gondii infection. Sera were examined for antibodies to T. gondii by the modified agglutination test (MAT); 50 of 51 (98%) were seropositive with titers of 20 in four,40 in four, 80 in one, 100 in eight, 200 in 17, 400 in 11, 800 or higher in five. Hearts of 43 seropositive dogs were bioassayed in mice. Viable T. gondii was isolated from 22 dogs; these isolates were designated TgDogEg1 to TgDogEg22. DNA isolated from cell culture derived tachyzoites of 20 of 22 isolates was genotyped using 10 PCR-restriction fragment length polymorphism markers (SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico). The results revealed three genotypes and one mixed infection. The three genotypes are ToxoDB PCR-RFLP #2 (Type III, four isolates), #3 (Type II variant, nine isolates) and #20 (six isolates) These results revealed the dominance of clonal Type II, III and ToxoDB #20 lineages of T. gondii in stray dogs from Giza, Egypt.